1. The Field of the Invention
The present invention generally relates to x-ray generating devices. In particular, the present invention relates to a high voltage connector that reduces the likelihood of electrical arcing during operation of the x-ray device.
2. The Related Technology
X-ray generating devices are extremely valuable tools that are used in a wide variety of applications, both industrial and medical. For example, such equipment is commonly employed in areas such as medical diagnostic examination and therapeutic radiology, semiconductor manufacture and fabrication, and materials analysis.
Regardless of the applications in which they are employed, x-ray devices operate in similar fashion. In general, x-rays are produced when electrons are emitted, accelerated, and then impinged upon a material of a particular composition. This process typically takes place within an evacuated enclosure of an x-ray tube. Disposed within the evacuated enclosure is a cathode, or electron source, and an anode oriented to receive electrons emitted by the cathode. The anode can be stationary within the tube, or can be in the form of a rotating annular disk that is mounted to a rotor shaft that, in turn, is rotatably supported by a bearing assembly. The evacuated enclosure is typically contained within an outer housing, which also serves as a coolant reservoir.
In operation, an electric current is supplied to a filament portion of the cathode, which causes a cloud of electrons to be emitted via a process known as thermionic emission. A high voltage potential is placed between the cathode and anode to cause the cloud of electrons to form a stream and accelerate toward a focal spot disposed on a target surface of the anode. Upon striking the target surface, some of the kinetic energy of the electrons is released in the form of electromagnetic radiation of very high frequency, i.e., x-rays. The specific frequency of the x-rays produced depends in large part on the type of material used to form the anode target surface. Target surface materials with high atomic numbers (“Z numbers”) are typically employed. The target surface of the anode is oriented so that the x-rays are emitted through windows defined in the evacuated enclosure and the outer housing. The emitted x-ray signal is then directed toward an x-ray subject, such as a medical patient, so as to produce an x-ray image.
In order to provide the high voltage potential that exists between the anode and the cathode, as well as to power the filament, the cathode is connected to an electrical power source via a high voltage cable. The high voltage cable is coupled to the x-ray tube via a high voltage connector. One type of connector is known as a pancake connector. Named because of its flattened, cylindrical shape, a pancake connector receives the high voltage cable through an opening disposed in the connector housing. The high voltage cable electrically connects within the connector housing to a centralized socket assembly that is configured to mate with electrical terminals disposed in a receptacle of the x-ray tube cathode. The socket assembly is electrically isolated from the connector housing by an insulating material disposed therebetween.
In greater detail, the socket assembly of the pancake connector typically comprises a metallic sleeve having an insulative potting material disposed within the interior of the sleeve. Electrical leads from the high voltage cable pass through the potting material and connect with sockets disposed on an exposed face of the socket assembly for mating with the electrical terminals of the cathode receptacle. An insulated gasket is typically disposed between the cathode receptacle and the pancake connector to further facilitate the mating of the socket assembly with the receptacle.
One particularly important application for x-ray devices such as that described above involves explosives detection by luggage inspection equipment and other related apparatus. X-ray devices are employed in explosives detection applications to examine luggage and packages in order to detect enclosed objects having a spectra that is indicative of explosive material. Such detection forms an important part of counterterrorism activities at critical locations such as airports, where personal safety and protection is paramount.
In order to accurately detect explosive material according to its spectra, the x-ray tube must be operated at relatively high operating voltages. For instance, an x-ray tube operating at 150 kV typically has a 2% false-positive rating, meaning that it erroneously detects a non-explosive for an explosive two out of every hundred scans. In contrast, the false-positive rating of a similar x-ray tube operating at 160 kV is in the range of less than one percent. Thus, higher operating voltages enable x-ray tubes to detect explosive material with more precision, resulting in quicker and more accurate scans.
Unfortunately, increasing the operating voltage of an x-ray tube also increases the incidence of voltage-related problems. One of these problems is electrical arcing. Electrical arcing represents a breakdown of the voltage potential within the tube. High voltage connectors, including pancake connectors, are especially susceptible to this undesirable side effect that is coincident with tube operation at higher power levels. For instance, electrical arcing can occur between the socket assembly, which is held at a high voltage potential, and the connector housing, which is at ground potential. Electrical arcs within the connector often emanate from locations called triple junctions, which are formed where a metallic component, an insulating component, and air meet. For instance, in one known connector design, a triple junction that is especially susceptible to arcing is formed at a point where the insulating material of the connecter housing, air, and a metallic coating applied near the socket assembly meet. In another known connector design, a triple junction is formed at a junction of the cathode receptacle, air, and the insulated gasket. These and other known pancake connector configurations have not been designed so as to adequately minimize the concentration of the electric field near triple junctions in the connector, which field concentration has been shown to increase the likelihood of a catastrophic arc during tube operation. Because it can severely damage tube components and render the x-ray device inoperable, arcing must be prevented.
The challenges described above in connection with electrical arcing across the high voltage connector are further exacerbated by the fact that known connector designs often include sharp, discontinuous features at or adjacent to the triple junctions. These sharp features, such as portions of the metallic sleeve of the socket assembly or the cathode receptacle that are near a triple junction, tend to increase the likelihood that arcing will occur. Though modifying the location and configuration of triple junctions, known pancake connector configurations have nonetheless failed to adequately reduce the likelihood for electrical arcing near such junctions during tube operation at elevated power levels.
In light of the above, a need exists to provide a high voltage connector that is designed so as to avoid the problems described above. Specifically, there is a need for a high voltage connector for use in devices, such as x-ray tubes, that provides adequate high power voltage potentials to the device without suffering electrical breakdown or increasing the likelihood of electrical arcing across the connector. Any solution should enable the x-ray tube to be operated at high power levels for use in applications such as the detection of explosive materials in packages, containers and the like.